The laser has been recognized as having utility in isotope separation by creating an excitation of one particular isotope without corresponding excitation of a different isotope of the same material. The excitation may be either of electrons in the various orbital states about the atom as, for example, illustrated in U.S. Pat. No. 3,772,519, assigned to the same assignee as the present application, or may be vibrational excitation as shown in United States patent application Ser. No. 514,303, filed Oct. 15, 1974, and also assigned to the same assignee as the present application. Isotopically selective excitation of electron orbital states is typically employed in a process of isotopically selective ionization with the result that the desired isotope type particles are given an electrical charge distinct from the particles of other isotope types that permits their physical separation through interaction with electrical, magnetic or combined fields. In the case of vibrational excitation, it has been proposed to modify the accommodation coefficient through vibrational excitation of a selected isotope type molecule such that in the process of diffusion of molecules of a mixture of isotopes through narrow diffusion chambers, the vibrationally excited isotope will accommodate or stick less readily to the channel walls and thereby diffuse at a higher rate, substantially increasing diffusion efficiency.